Thermodynamic characteristics, microstructure and mechanical properties of Sn-0.7Cu-xIn lead-free solder alloy

The microstructure and mechanical properties of Sn-0.7Cu solder alloy and Sn-0.7Cu with 1.0e5.0 wt% indium addition were investigated in this study. With indium added into Sn-0.7Cu solder, the melting temperature decreased and the reaction temperature increased. Coarse grains of Cu-6(Sn,In)(5) intermetallic compounds (IMCs) were formed in the alloy matrix when the indium content increased to 1.0 wt%. Indium was evenly distributed in the beta-Sn phase and Cu-6(Sn,In)(5) IMCs in as-prepared In-containing solder alloys. After isothermal aging, indium accumulated gradually in the Cu-6(Sn,In)(5) IMCs while decreasing its content in the beta-Sn phase. Tensile test results indicated that the ultimate tensile strength increased obviously and that the elongation decreased significantly with indium addition. Sawtooths were observed in the stress-strain curves of all aged In-containing alloys. A model describing a coherent relationship between the beta-Sn phase and the Cu-6(Sn,In)(5) phase was proposed to explain this phenomenon. The fracture surface of the Sn-0.7Cu alloy exhibited a ductile fracture mode while a mixed ductile-brittle fracture mode occurred when excessive indium was added into Sn-0.7Cu alloys. (c) 2018 Elsevier B.V. All rights reserved.